linux-kernel - Re: [PATCH 1/6] perf, x86: Basic Haswell LBR call stack support

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Date:	Mon, 22 Oct 2012 13:23:23 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	"Yan, Zheng" <zheng.z.yan@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH 1/6] perf, x86: Basic Haswell LBR call stack support

On Mon, Oct 22, 2012 at 12:33 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>
> On Mon, 2012-10-22 at 14:11 +0800, Yan, Zheng wrote:
> > +       /* LBR callstack does not work well with FREEZE_LBRS_ON_PMI */
> > +       if (!cpuc->lbr_sel || !(cpuc->lbr_sel->config & LBR_CALL_STACK))
> > +               debugctl |= DEBUGCTLMSR_FREEZE_LBRS_ON_PMI;
>
Is this a bug or a feature?

>
> How useful it is without this? How many calls between PMI and us getting
> to intel_pmu_lbr_read()?

Agreed with Peter. Freeze on PMI is critical for LBR in general.
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